1. Field of the Invention
This invention relates to an image display system, and more particularly to a system for displaying an image subjected to, for instance, dynamic range compression processing.
2. Description of the Related Art
There have been put into practice a CT (Computed Tomography) apparatus or an MRI (Magnetic Resonance Imaging) apparatus for showing in a slice a predetermined part of an object such as a human body. Generally a plurality of cross-sectional images of an object taken at different depths (in the direction perpendicular to the plane of the image) are obtained by the use of such an apparatus in order to know the three-dimensional conditions of the part.
The cross-sectional images are generally recorded as hard copies or displayed by, for instance, a CRT display after subjected to gradation processing so that they are adapted for reading.
In a medical image displayed by, for instance, a CRT, a plurality of areas of interest can be sometimes included. In such a case, the optimal processing condition generally differs by the area of interest. For example, in a chest CT image, the lung and the mediastinum are different in the optimal gradation processing condition. Conventionally, when an image includes a plurality of areas of interest, a plurality of images processed under different gradation processing conditions are displayed. For example, in the case of a chest CT image, an image gradation-processed under a processing condition suitable for reproducing an image adapted to reading the lung and an image gradation-processed under a processing condition suitable for reproducing an image adapted to reading the mediastinum are displayed side by side in one screen.
In the case where only one cross-section of the object part is displayed, displaying two images processed under different conditions in a screen gives rise to no problem in reading. However, in the case where a number of cross-sections of the object part are displayed in sequence, displaying two images processed under different conditions in a screen for each cross-section makes reading troublesome. That is, when reading the images, the reader must change the direction of his or her eyes from one image to the other on one screen each time the images of a different cross-section are displayed (generally requiring movement of his or her neck), which is very troublesome for the reader.